The invention concerns an induction transponder detection and reading apparatus and the operative method through which the transit of the authorized transponders through a controlled passage is detected.
Induction transponder readers, hereinafter called for simplicity xe2x80x9ctransponder readersxe2x80x9d, which interact in the controlled passage with the transponders authorized to transit, are already known. Said transponder readers in the first case emit a continuous electromagnetic field and us one or two distinct coils with functions of transmitter and receiver. In the second case they emit a periodic intermittent electromagnetic field and they use two distinct transmitting and receiving coils, or only one coil that is made to operate alternatively as transmitter and receiver. Said coil or coils are placed on the facing sides of the transit passage or are wrapped around the passage to be controlled, while the induction transponder, with which they interact, contains a receiving/transmitting circuit which is stimulated every time it enters the field produced by the transmitting antenna and which interacts with a coded signal which is received by the antenna that acts as a receiver. After the signal has been read and decoded, it is sent to an associated circuit group that has the appropriate functions based on the results which the transponder reader and associated circuit group must reach.
For example, the said associated group, can control the opening of certain gates, it can reduce the discriminating sensitivity of metal detectors (Italian patent n. 1.271.382), it can memorize the number or the code and therefore the person associated with this transponder and the time at which said transit was made, or it can execute other functions. The known transponder readers therefore, allow contact free reading and are also called hands free electronic card readers since they allow the possessor of the authorized electronic card to transit through the controlled passage without having to stop for reading operations which require a physical contact between the card and the apparatus. These types of transponder readers operate in a field of frequencies that are normally between 50 and 450 KHz to allow the use of small sized electronic cards or transponders, with compact internal coils.
The activation of the transponders without internal batteries requires a high intensity value of the electromagnetic field in the whole controlled passage, including the areas that are the furthest away from the antennas. This means that there are high value electromagnetic fields in the proximity of the transmitting antenna, so as to make the transponder readable and maintain the dialogue with it, throughout the controlled passage, even when the transponder is aimed, in respect to the flow of waves from the transmitting antenna, in minimal coupling conditions.
The high intensity of the effective value of the electromagnetic field required to stimulate the transponder, whether it emits a continuous electromagnetic field, or if it emits an intermittent electromagnetic field with the antenna that operates alternately as a transmitter and a receiver, is necessary to activate the electronic card that is enabled by the transponder reader, even when it transits in particularly critical positions of orientation. The known hands free transponder readers require therefore an effective irradiated electromagnetic field value in the controlled passage that is decidedly higher than the limits set by the World Health Organization at 0.66 A/m (at 125 KHz) defined as the electromagnetic field to which the human body can be exposed, even for relatively short periods, without causing damaging effects.
A lowering of the electromagnetic field""s effective values, in the controlled passage, to values that are on average lower or equal to those indicated by the World Health Organization would make the authorized electronic cards undetectable, unless these are made to transit in close proximity to the transmitting coil.
The object of the present invention is to provide a transponder reader structure and a method of managing the electromagnetic field in the controlled passage, which will allow the detection and reading of authorized electronic cards or transponders, with the use of electromagnetic fields with on average a minimal intensity and energy, that is in any case lower than the maximum indicated by the World Health Organization, so that it will not harm people who cross the same controlled passage, even repeatedly, but which in any case will be capable of activating the authorized electronic cards or transponders, which ever way they are oriented, inside the controlled passage in which the detection and reading takes place.
The invention that has made the attainment of these results possible is embodied in a transponder detection and reading apparatus and in the operational method with which its operations are controlled. It consists in a programmed detection-reading apparatus which controls a group that includes the transmitting coil, which is operated repeatedly so that each time it emits a detection electromagnetic field which is sufficiently intense only for a brief interval of the period of the transmission signal, defined also as the presence detection interval, but which is sufficient to permit the detection of the transponders transiting in the controlled passage, irrespective of their orientation, and to make them emit a transponder presence signal. Consequently, following the start of the transit of a transponder in the controlled passage and of the detection of the transponder presence signal emitted by it, when it is invested by the electromagnetic detection field even though briefly, the group which includes the transmitting coil is commanded to emit a prolonged electromagnetic field for a duration interval that is sufficient to completely activate the transponder, defined as the reading interval, so that the transponder emits its own complete coded signal so that it can be read, decoded and recognized. Subsequently, the group which includes the transmitting coil is commanded repeatedly to emit an electromagnetic field that remains brief each time (presence detection interval) for the time in which the identified transponder remains in the detection space, that is in the controlled passage, so as to obtain from the transponder in transit only the emission of the transponder presence signal. At the termination of the detection of the transponder presence signal in the controlled passage, for a programmed time interval, the apparatus, which controls the group that includes the transmitting coil, resets itself to control this group again and allow the detection and reading of a new transponder in transit. The advantages offered by the invention consist in the fact that for each transmission period of the transponder detection-reading apparatus, only for a small fraction of this (presence detection interval) do we have a noticeable irradiation of electromagnetic waves and therefore of energy in the controlled passage, whose effective value, in relation to the entire period, move decidedly towards zero, therefore towards a value that, operating on the emission intervals and on the transmission period of the group including the transmitting coil of the transponder detection-reading apparatus, can be led to a value that is much lower than the maximum value indicated by the World Health Organization.
One of the elements of the invention involves discovery that brief intervals of emission of an adequately intense electromagnetic field (presence detection intervals) are sufficient to make the transiting transponder emit a presence signal, whose first detection commands the circuit including the transmitting coil of the transponder detection and reading apparatus to emit an electromagnetic field of longer duration, that is sufficient to completely activate the transponder (reading interval) so that its emits the whole coded response signal. The reading of the latter, by means of the receiver circuit of the transponder detection-reading apparatus, permits the identification of the transponder and therefore allows the issue of successive instructions to the external equipment to be controlled. It also commands the reduction, at least of the duration, of the sufficiently intense electromagnetic field that is emitted by the circuit which includes the transmitting coil of the said detection-reading apparatus, only for the presence detection interval in each transmission period, as long as the transponder remains in the controlled passage. Upon the termination of the reception of the transponder presence signal in the controlled passage, when the transponder has passed through it, the programmed apparatus which controls the activity of the circuit comprising the transmitting coil of the transponder detection-reading apparatus, resets itself and commands this circuit to emit short lasting electromagnetic fields (presence detection intervals) while awaiting to receive the first presence signal from the next transponder in transit.
The described operative method and the programmed apparatus which control the entire transponder detection-reading apparatus therefore allow the activation of the group comprising the transmitting coil only for brief time periods (presence detection intervals), and only for a longer lasting period (reading interval) when the transponder is introduced into the controlled space and emits its first presence signal. On average therefore, only for a brief fraction of the effective period of the transmission signal do we have the emission of an electromagnetic field that is sufficiently intense, with a marked decrease in the effective value of the same in relation to the entire period of the transmission signal, so as to bring it down to a value that is markedly lower than that indicated by the World Health Organization.